Conventionally, in an electric throttle in which a throttle valve is driven by a motor, a method for an abnormality determination of a rotation angle sensor detecting an actual opening angle of the throttle valve is well known. According to JP-H06-42907 (U.S. Pat. No. 5,544,000 A), a difference ΔV between detected values of two rotation angle sensors is compared with a standard value ΔV0. When a state that the difference ΔV is greater than the standard value ΔV0 has continued for a period greater than or equal to a predetermined period, the rotation angle sensor is determined to be abnormal.
However, the rotation angle sensor for detecting abnormality is necessary to be different from the rotation angle sensor detecting the actual opening angle of the throttle valve. Since two rotation angle sensors are necessary, a cost of the electric throttle becomes greater.